Flow over a Magnetically Suspended Cylinder in an Axial Free Stream

(y - D/2)/delta
2.0
1.5
1.0
0.5
L/D=4.13 (45Dia.) delta=32.5mm
L/D=5.02 (45Dia.) delta=32.5mm
L/D=6.00 (25Dia.) delta=19.0mm
L/D=8.13 (45Dia.) delta=41.0mm
0.2
0.0
0 0 0 0 1 1 1 1
u/U
Figure 6. u/U vs.[y-(D/2)]/δ, effect of fineness ratio)
(Re D =50,000 for 25mm dia, 100,000 for 45mm dia.)
2.0
1.5
L/D=4.13 (45Dia.) delta=32.5mm
L/D=5.02 (45Dia.) delta=32.5mm
L/D=6.00 (25Dia.) delta=19.0mm
L/D=8.13 (45Dia.) delta=41.0mm
(y - D/2)/delta
1.0
0.2
0.5
0.0
0 0 0 0
0.8
u rms /U
Figure 7. u rms /U vs. .[y-(D/2)]/δ, effect of fineness ratio
The boundary layer leaving the cylinder at the trailing edge was further investigated for various fineness ratios.
The mean velocity profiles and the turbulence intensity normalizes by the boundary layer thickness are shown in Fig.
6 and Fig. 9, respectively. Ota 4 investigated the boundary layer over a sting-mounted sharp-edged cylinder, and his
velocity profiles at x/D=3.1, 5.1, and 7.1 from the leading edge are very consistent with the present data at the
trailing edge (L/D=4.13-8.13). Ota’s experiment corresponds to Re D =5.62x10 4 and the Reynolds number for the
measurements in Figs. 6 and 7 was 5x10 4 for the 25mm cylinder and 1x10 5 for the 45mm cylinder. The oil flow
visualization and Ota’s measurement indicated a separation bubble from the leading edge ending with flow
reattachment approximately at 1.5-1.6 diameter downstream. The mean velocity profiles further downstream of the
reattachment are indicative of a developing turbulent boundary layer. The turbulent intensity profiles are also in
general agreement between the two experiments, though the present data are at a somewhat higher level. The power
spectrum density in the immediate wake shear layer showed the distribution typical of turbulent boundary layer
devoid of any spectral peak, but at x/D=4, a spectral peak was evident at Strouhal number fD/U=0.185 which was
indicative of a helical mode wake oscillation.
C. Force Measurement
The magnetic balance was calibrated against the known weight for each model. The uncertainty of the drag
coefficient measurement at Reynolds number 10 5 , for example, was estimated to be ±0.005.
- 5 –
American Institute of Aeronautics and Astronautics